I will be on vacation next week so this will be the last forecast until Monday, January 23.
Summary and Analysis:
A trough in the upper-level wave pattern is propagating slowly eastward toward the Northeast this afternoon. A cold front at the leading edge of this trough is lifting the mild, moist air over us as it moves eastward, thus the rain this afternoon……
Just a minor digression here….. When I mention a front this time of year it is usually a surface representation of what we call the polar front, which is where the strongest temperature gradient in the Northern Hemisphere is located, separating very cold air to the north from much warmer air to the south. The jet stream forms at upper-levels along this polar front, the strong winds being generated by a steep pressure gradient created by the temperature gradient (warm air is lighter than cold air and pressure is just the weight of the air above a point). We name the surface fronts (surface representation of this polar front) either a cold or warm front depending on which way the polar front is moving. If the cold air is advancing (polar front moving south and east, at the leading edge of a trough in the wave pattern of the polar front) it is called a cold front. If warm air is advancing (polar front moving north and east, at the leading edge of a ridge in the wave pattern), we call it a warm front. When a cold front passes, the cold air within the trough, north of the polar front, moves in and temperatures drop. The opposite occurs after a warm front passes, the warm air to the south of the polar front (associated with the ridge) moves in and temperatures rise…..
……The cold front will move through this evening and temperatures will drop precipitously overnight. It will also become windy as the pressure gradient steepens. This pressure gradient is due to strong surface high pressure associated with the western side of the trough building eastward. As a result, it will turn dry but windy and much colder tonight into the weekend. As the trough propagates eastward over the weekend the surface high pressure system will build over the region. This will result in beautiful winter days with seasonable temperatures on Sunday and Monday. The only fly in the ointment is on Saturday. The southern edge of the trough, represented as a stationary front (polar front), will be located over the Middle Atlantic states. Warmer air and moisture overriding this front will be creating cloud cover, with snow and ice over southern PA, MD and NJ Saturday morning. This precipitation, in the form of snow may make it far enough north to give Berkshire County a snow shower late in the day, but I believe it is more likely that we will just have a cloudy and cold day and will stay dry.
Unfortunately, if you are either a snow or winter lover, fortunately if you don’t like cold and snow, the trough will lift out early next week and a broad ridge in the wave pattern will build over almost the entire US, with the polar front shifting north well into Canada. As a result, temperatures will again become unseasonably mild midweek, probably through next weekend. Any precipitation that falls during that time will be in the form of rain.
Berkshire County Forecast
Thursday Night
A few lingering light showers early this evening, then remaining mostly cloudy overnight. It will turn windy and much colder. There is the chance of a snow flurry or snow shower toward morning with little or no accumulation. Temperatures will be near 50 into the lower 50s this evening. Temperatures will start a precipitous drop from north to south beginning about 11 pm with temperatures falling into the upper 20s to near 30, mid 20s over the elevated terrain, by morning. Southwesterly winds at 10 – 15 mph early will shift to west-northwesterly late in the evening and increase to 10 – 20 mph, 15 -25 mph over the elevated terrain.
Friday
Mostly cloudy with the chance of a flurry or snow shower early then becoming mostly sunny. It will be windy and much colder than previous days. Probability of precipitation 30% early, little or no snow accumulation. Temperatures will hold steady in the upper 20s to near 30 in the lower elevations of central and northern Berkshire (e.g. Pittsfield, North Adams), low 30s over the lower elevations of South County (e.g. Great Barrington), mid 20s over the elevated terrain into early afternoon, then fall through the 20s during the afternoon. West-northwest winds at 15 – 25 mph. Wind chill temperatures in the teens during the afternoon.
Friday Night
Partly cloudy and cold with diminishing winds. Low temperatures in the mid to upper single digits, near 10 in South County, mid single digits over the elevated terrain. Northwesterly winds at 10 – 15 mph in the evening, becoming light after midnight.
Saturday
Mostly cloudy and cold. There is the chance of a snow shower late. Probability of precipitation 30%. Little or no accumulation. High temperatures in the mid 20s over the lower elevations of central and northern Berkshire, mid to upper 20s in South County, and low 20s over the elevated terrain. Light south-southwesterly winds.
Saturday Night
Chance of a flurry or snow shower early, then clearing skies and not as cold. Low temperatures in the mid to upper teens. Light south-southwesterly winds becoming northwesterly at 5 – 10 mph after midnight.
Sunday
Mostly sunny with seasonable temperatures and a light northwesterly breeze. High temperatures near 30, low 30s in the lower elevations of South County and mid to upper 20s over the elevated terrain. Northwesterly winds at 5 – 10 mph.